title: Functional characterization of protein 4.1 homolog in amphioxus: defining a cryptic spectrin-actin-binding site.
abstract: Vertebrate 4.1 proteins have a spectrin-actin-binding (SAB) domain, which is lacking in all the invertebrate 4.1 proteins indentified so far, and it was therefore proposed that the SAB domain emerged with the advent of vertebrates during evolution. Here we demonstrated for the first time that amphioxus (an invertebrate chordate) protein 4.1, though lacking a recognizable SAB, was able to bind both spectrin and actin, with a binding capacity comparable to that of human protein 4.1. Detailed structure-activity analyses revealed that the unique domain U2/3 was a newly identified SAB-like domain capable of interacting with spectrin and actin, suggesting the presence of a "cryptic" SAB domain in amphioxus 4.1 protein. We also showed that amphioxus 4.1 protein gene was the common ancestor of vertebrate 4.1 protein genes, from which 4.1R, 4.1N, 4.1G, and 4.1B genes originated. This work will encourage further study on the structure-activity of invertebrate 4.1 protein and its interacting proteins.
authors.affiliation: 1] Laboratory for Evolution & Development, Institute of Evolution & Marine Biodiversity and Department of Marine Biology, Ocean University of China, Qingdao 266003, China [2].
authors.forename: Lixia
authors.initials: L
authors.lastname: Wang
authors.forename: Yuan
authors.initials: Y
authors.lastname: Wang
authors.forename: Zhaohe
authors.initials: Z
authors.lastname: Li
authors.forename: Zhan
authors.initials: Z
authors.lastname: Gao
authors.forename: Shicui
authors.initials: S
authors.lastname: Zhang
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D015870:Gene Expression; D023061:Gene Order; D064175:Lancelets / Q000235:genetics* / Q000378:metabolism*; D009928:Organ Specificity; D010802:Phylogeny; D011485:Protein Binding; D017422:Sequence Analysis, DNA; D013049:Spectrin / Q000378:metabolism
chemical_list: D000199:Actins; D003598:Cytoskeletal Proteins; D013049:Spectrin